When cutting an object such as a metal mold by a Numerical Control (NC) tool machine, it is necessary to generate data for the NC tool machine (hereafter, called “NC data”). The NC data includes path data of roughing tool, for example, and a Computer Aided Manufacturing (CAM) software is ordinarily used for the generation of the NC data. For example, a user in charge of the generation of the NC data selects any roughing type based on his or her own experience from some roughing types (e.g. contour parallel offset roughing, holing, plane stepping, pencil cut, and etc. As for the details, see Byoung K. Choi et al., Sculptured Surface Machining: Theory and Applications, Chapter 7, KLUWER ACADEMIC PUBLISHERS, January 1999, ISBN: 0412780208) that are supported by the CAM software. Then, the CAM software carries out a tool path calculation processing based on the roughing type selected by the user to generate the NC data.
Incidentally, technology to estimate a load to the tool in the machining is disclosed, for example, in Shinji Iwata, Hideki Aoyama “Module to estimate cutting resisting power”, lecture papers of Die and Mold engineer conference 2001, Die and Mold technology committee, Jun. 24, 2001, p200–201.
However, when roughing the metal mold, for example, there are a lot of cases where the cutting load is not flat, and it is difficult to achieve the effective machining by the aforementioned conventional methods. Namely, when the roughing for the whole metal mold is carried out by only the specific roughing type selected by the user, unless the form of the metal mold after the machining is a simple form such as a cube, the load is concentrated to the tool when machining a specific portion of the metal mold. Then, when the object including such a portion that causes the high load is machined, it is necessary to slow down the feed rate in order to prevent damage and vibration of the tool, and the time necessary to machine the metal mold becomes increased as a whole.